The invention is broadly suited for lighting any face or dial requiring such light, and especially instruments found on the instrument panel of an aircraft. The invention is even more aptly designed for military aircraft, e.g. helicopters, which are used for night flying by pilots wearing night vision goggles.
Eyebrow lighting is one method presently used for illuminating the faces or dials of instruments on military helicopters, such lighting so-called because a plurality of small incandescent lamps are positioned only around the vertically uppermost perimeter of each instrument. Instruments using such incandescent lighting have been found to be unreadable by pilots wearing night vision goggles, because of the non-uniformity of light which results when the intensity of the incandescent lamps is reduced to a low enough level to be used with night vision goggles which amplify and enhance low level lighting thousands of times. Moreover, it has been found that such lighting produces undesirable reflections within the canopy of the aircraft.
Other instrument installations have employed light reflecting wedges to direct light across the faces of the instruments. The source of light used, however, are incandescent lamps which produce undesirable low intensity lighting, as previously indicated. The invention is directed to the provision of a lighting fixture which is especially designed to produce improved illumination with reduced glare at low intensity levels of light.
Briefly stated, the invention is in a lighting fixture which is mounted on an instrument having a face or dial which is desired to be illuminated. The fixture comprises, a housing having a centrally disposed opening extending therethrough, and an inner cylindrical wall which is adjacent the opening, being spaced slightly outwardly therefrom, and around which is located an electroluminescent lamp. A cylindrical layer of micro-louver type material is placed over the electroluminescent (EL) lamp to prevent an observer of the instrument from seeing the light ring that is created around the face of the instrument by the EL lamp and to eliminate the undesired reflections within the aircraft canopy. A film is placed over the EL lamp between the lamp and louver material to polarize the light emitting from the lamp to eliminate the reflection of light from the glass of the instrument, thereby reducing glare from the instrument.
It has been found that the lighting fixture of the invention provides highly improved and uniform illumination of the face of the instrument. Further, the lighting fixture can be operated at a high enough intensity for direct viewing, or at a sufficiently low intensity for satisfactory viewing through night vision goggles. The electroluminescent lamps produce little, if any, infrared energy which is characteristic of incandescent lamps and which can create too much spectral energy in some areas to reduce the resolution potential of the night vision goggles.